C-terminal phosphorylation of Hsp70 and Hsp90 regulates alternate binding to co-chaperones CHIP and HOP to determine cellular protein folding/degradation balances

Rapid deacetylation of yeast Hsp70 mediates the cellular response to heat stress

Hsp70 is a highly conserved molecular chaperone critical for the folding of new and denatured proteins. While traditional models state that cells respond to stress by upregulating inducible HSPs, this response is relatively slow and is limited by transcriptional and translational machinery. Recent studies have identified a number of post-translational modifications (PTMs) on Hsp70 that act to fine-tune its function. We utilized mass spectrometry to determine whether yeast Hsp70 (Ssa1) is differentially modified upon heat shock. We uncovered four lysine residues on Ssa1, K86, K185, K354 and K562 that are deacetylated in response to heat shock. Mutation of these sites cause a substantial remodeling of the Hsp70 interaction network of co-chaperone partners and client proteins while preserving essential chaperone function. Acetylation/deacetylation at these residues alter expression of other heat-shock induced chaperones as well as directly influencing Hsf1 activity. Taken together our data suggest that cells may have the ability to respond to heat stress quickly though Hsp70 deacetylation, followed by a slower, more traditional transcriptional response.

ERK-dependent phosphorylation of the linker and substrate-binding domain of HSP70 increases folding activity and cell proliferation

The enhanced productive folding of translated polypeptides by heat shock protein 70 (HSP70) is often required for the survival of cancer cells. Although the folding activity of HSP70 is considered a significant determinant of the progression of cancer cells, it is still unknown how this activity could be regulated. Here, we report that the phosphorylation of HSP70 facilitates its folding activity, enhancing cell proliferation. Mass spectrometry identified the serine residues at positions 385 and 400 in the linker and substrate-binding domains of HSP70, respectively, as sites of phosphorylation mediated by EGF signaling, and this result was further confirmed by site-directed mutagenesis. ERK is known to be a specific kinase. The phosphorylation of the two sites induces the extended conformation of HSP70 via the regulation of the binding of the linker to the nucleotide- and substrate-binding domains, augmenting the binding affinity of HSP70 to substrates and enhancing its folding activity; this ultimately results in pro-proliferative effects. Cell lines harboring activated ERK showed increased phosphorylation of HSP70, and a positive correlation between the phosphorylation of HSP70 and the activity of ERK was observed. Thus, this study demonstrated that the ERK-dependent phosphorylation of HSP70 facilitated its folding activity and cellular proliferative function.

Decreased OLA1 (Obg-Like ATPase-1) Expression Drives Ubiquitin-Proteasome Pathways to Downregulate Mitochondrial SOD2 (Superoxide Dismutase) in Persistent Pulmonary Hypertension of the Newborn

Persistent pulmonary hypertension of the newborn (PPHN) is a failure of pulmonary vascular resistance to decline at birth rapidly. One principal mechanism implicated in PPHN development is mitochondrial oxidative stress. Expression and activity of mitochondrial SOD2 (superoxide dismutase) are decreased in PPHN; however, the mechanism remains unknown. Recently, OLA1 (Obg-like ATPase-1) was shown to act as a critical regulator of proteins controlling cell response to stress including Hsp70, an obligate chaperone for SOD2. Here, we investigated whether OLA1 is causally linked to PPHN. Compared with controls, SOD2 expression is reduced in distal-pulmonary arteries (PAs) from patients with PPHN and fetal-lamb models. Disruptions of the SOD2 gene reproduced PPHN phenotypes, manifested by elevated right ventricular systolic pressure, PA-endothelial cells apoptosis, and PA-smooth muscle cells proliferation. Analyses of SOD2 protein dynamics revealed higher ubiquitinated-SOD2 protein levels in PPHN-lambs, suggesting dysregulated protein ubiquitination. OLA1 controls multiple proteostatic mechanisms and is overexpressed in response to stress. We demonstrated that OLA1 acts as a molecular chaperone, and its activity is induced by stress. Strikingly, OLA1 expression is decreased in distal-PAs from PPHN-patients and fetal-lambs. OLA1 deficiency enhanced CHIP affinity for Hsp70-SOD2 complexes, facilitating SOD2 degradation. Consequently, mitochondrial H₂O₂ formation is impaired, leading to XIAP (X-linked inhibitor of apoptosis) overexpression that suppresses caspase activity in PA-smooth muscle cells, allowing them to survive and proliferate, contributing to PA remodeling. In-vivo, ola1^-/- downregulated SOD2 expression, induced distal-PA remodeling, and right ventricular hypertrophy. We conclude that decreased OLA1 expression accounts for SOD2 downregulation and, therefore, a therapeutic target in PPHN treatments.

Fine Tuning: Effects of Post-Translational Modification on Hsp70 Chaperones

The discovery of heat shock proteins shaped our view of protein folding in the cell. Since their initial discovery, chaperone proteins were identified in all domains of life, demonstrating their vital and conserved functional roles in protein homeostasis. Chaperone proteins maintain proper protein folding in the cell by utilizing a variety of distinct, characteristic mechanisms to prevent aberrant intermolecular interactions, prevent protein aggregation, and lower entropic costs to allow for protein refolding. Continued study has found that chaperones may exhibit alternative functions, including maintaining protein folding during endoplasmic reticulum (ER) import and chaperone-mediated degradation, among others. Alternative chaperone functions are frequently controlled by post-translational modification, in which a given chaperone can switch between functions through covalent modification. This review will focus on the Hsp70 class chaperones and their Hsp40 co-chaperones, specifically highlighting the importance of post-translational control of chaperones. These modifications may serve as a target for therapeutic intervention in the treatment of diseases of protein misfolding and aggregation.

The Complex Phosphorylation Patterns that Regulate the Activity of Hsp70 and Its Cochaperones

Proteins must fold into their native structure and maintain it during their lifespan to display the desired activity. To ensure proper folding and stability, and avoid generation of misfolded conformations that can be potentially cytotoxic, cells synthesize a wide variety of molecular chaperones that assist folding of other proteins and avoid their aggregation, which unfortunately is unavoidable under acute stress conditions. A protein machinery in metazoa, composed of representatives of the Hsp70, Hsp40, and Hsp110 chaperone families, can reactivate protein aggregates. We revised herein the phosphorylation sites found so far in members of these chaperone families and the functional consequences associated with some of them. We also discuss how phosphorylation might regulate the chaperone activity and the interaction of human Hsp70 with its accessory and client proteins. Finally, we present the information that would be necessary to decrypt the effect that post-translational modifications, and especially phosphorylation, could have on the biological activity of the Hsp70 system, known as the “chaperone code”.

The N-terminal sequence of murine PRMT5 variant 2 is required for Hsp70 interaction and CHIP ligase-mediated degradation

Protein arginine methyltransferase PRMT5 synthesizes the symmetric dimethylarginine in nuclear and cytoplasmic proteins such as histone H2A, H4 and several non-histone proteins that are required for a variety of biological processes. Currently, two splice variants (v1 and v2) of murine PRMT5 have been deposited in the NCBI sequence database, in which PRMT5-v1 and -v2 contain different 33 and 16 amino acids at the N-terminal sequences, respectively. Here we showed that murine PRMT5-v1 is stable, but PRMT5-v2 is constantly degraded through both the ubiquitin proteasome system (UPS) and the autophagic-lysosomal pathway (ALP) in an N-terminal sequence-dependent manner. Furthermore, inhibition of UPS and ALP elevated the stability of PRMT5-v2 that made it localized in the nucleus and the cytoplasm. In addition, PRMT5-v2 exhibited the enzyme activity to catalyze histone H2A and H4 methylation. Notably, we found that the heat shock protein (Hsp) 70 specially recognizes the N-terminal sequence of PRMT5-v2 and the carboxyl terminus of Hsp70-interacting protein (CHIP) is required for poly-ubiquitination and the degradation of PRMT5-v2. These results suggest that Hsp70/CHIP chaperone-mediated protein degradation system is crucial in the regulation of PRMT5-v2 turnover, which has the potential to balance the symmetrical arginine dimethylation in cells.

Dynamic remodeling of the interactomes of Nematostella vectensis Hsp70 isoforms under heat shock

Heat shock protein 70s (Hsp70s) are a highly conserved class of molecular chaperones that fold a large proportion of the proteome. Nematostella vectensis (Nv) is an estuarine sea anemone that has emerged as a model species to characterize molecular responses to physiological stressors due to its exposure to diverse, extreme abiotic conditions. Previous transcriptional data has shown dramatic differences among expression profiles of three NvHsp70 isoforms (NvHsp70A, B and D) under stress but it is unknown if, and to what extent, the client proteins for these chaperones differ. In order to determine client specificity, NvHsp70A, B and D were expressed in Saccharomyces cerevisiae budding yeast lacking native Hsp70 and interacting proteins for each Hsp70 were determined with mass spectrometry in yeast ambient and heat shock conditions. Our analyses showed <50% of identified interacting proteins were common to all three anemone Hsp70s and 3-18% were unique to an individual Hsp70. Mapping of temperature induced interactions suggest that under stress a proportion of clients are transferred from NvHsp70A and NvHsp70D to NvHsp70B. Together, these data suggest a diverse set of interacting proteins for Hsp70 isoforms that likely determines the precise functions for Hsp70s in organismal acclimation and potentially adaptation. BIOLOGICAL SIGNIFICANCE: Although the Hsp70 family of molecular chaperones has been studied for >50 years, it is still not fully understood why organisms encode and express many highly-similar Hsp70 isoforms. The prevailing theory is that these isoforms have identical function, but are expressed under unique cellular conditions that include heat shock to cope with increased number of unfolded/misfolded proteins. The sea anemone Nematostella vectensis encodes three Hsp70 isoforms A, B and D that when expressed in yeast demonstrate unique functionalities. This study provides the interactome of NvHsp70s A, B and D and demonstrates that Hsp70 isoforms, while highly similar in sequence, have unique co-chaperone and client interactors.

The proteostasis network provides targets for neurodegeneration

The production, quality control, and degradation of proteins are a tightly controlled process necessary for cell health. In order to regulate this process, cells rely upon a network of molecular chaperone proteins that bind misfolded proteins and help them fold correctly. In addition, some molecular chaperones can target terminally misfolded proteins for degradation. Neurons are particularly dependent upon this "proteostasis" system, failures in which lead to neurodegenerative disease. In this review, we identify opportunities for modulating molecular chaperone activity with small molecules, which could lower the burden of misfolded protein within neurons, reducing cell death and ameliorating the effects of neurodegeneration. LINKED ARTICLES: This article is part of a themed section on Therapeutics for Dementia and Alzheimer's Disease: New Directions for Precision Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.18/issuetoc.

HSP70 is required for the proper assembly of pericentriolar material and function of mitotic centrosomes

Background

At the onset of mitosis, the centrosome expands and matures, acquiring enhanced activities for microtubule nucleation and assembly of a functional bipolar mitotic spindle. However, the mechanisms that regulate centrosome expansion and maturation are largely unknown. Previously, we demonstrated in an immortalized human cell line CGL2 and cancer cell line HeLa that the inducible form of heat shock protein 70 (HSP70) accumulates at the mitotic centrosome and is required for centrosome maturation and bipolar spindle assembly.

Results

In this study, we further show that HSP70 accumulated at the spindle pole in a PLK1-dependent manner. HSP70 colocalized with pericentrin (PCNT), CEP215 and γ-tubulin at the spindle pole and was required for the 3D assembly of these three proteins, which supports mitotic centrosome function. Loss of HSP70 disrupted mitotic centrosome structure, reduced pericentriolar material recruitment and induced fragmentation of spindle poles. In addition, HSP70 was necessary for the interaction between PCNT and CEP215 and also facilitated PLK1 accumulation and function at the spindle pole. Furthermore, we found that HSP70 chaperone activity is required for PCNT accumulation at the mitotic centrosome and assembly of mitotic spindles.

Conclusion

Our current results demonstrate that HSP70 is required for the accurate assembly of the pericentriolar material and proper functioning of mitotic centrosomes.

Tomm34 is commonly expressed in epithelial ovarian cancer and associates with tumour type and high FIGO stage

Background

Increased activity of the chaperones Hsp70 and Hsp90 is a common feature of solid tumours. Translocase of the outer mitochondrial membrane 34 (Tomm34) is a cochaperone of both Hsp70 and Hsp90 that was found to be overexpressed in colorectal, hepatocellular, lung and breast carcinomas. The expression profile of Tomm34 in ovarian cancer has not been investigated. Therefore, the aim of the current study was to investigate the expression pattern of Tomm34 in ovarian carcinomas and analyse its correlation with clinico-pathological parameters.

Results

Epithelial ovarian cancers (140) were histologically classified based on their morphology and graded into two types comprising 5 histologic subgroups. Type I carcinomas comprise low grade serous (LGSC), clear cell (CCOC) and endometrioid (ENOC), type II comprises high grade serous carcinomas (HGSC) and solid, pseudoendometrioid, transitional carcinomas (SET). Tomm34 was more highly expressed in type II than type I carcinomas (p < 0.0001). Comparing tumours based on the mutation in the TP53 gene revealed similar results, where mutant tumours exhibited significantly higher levels of Tomm34 (p < 0.0001). The decreased levels of Tomm34 in type I carcinomas were particularly evident in clear cell and mucinous carcinomas. The expression of Tomm34 was also positively correlated with FIGO stage (r = 0.23; p = 0.007). Tomm34 levels also indicated poor prognosis for patients with mutant p53.

Conclusions

Our data indicate that Tomm34 is commonly expressed at high levels in epithelial ovarian cancers, except for the clear cell and mucinous subtypes. The expression of Tomm34 corresponds with the dualistic model of ovarian cancer pathogenesis where high grade, type II tumours exhibit higher expression of Tomm34 in contrast to type I tumours. These data are also comparable to the previous findings that Tomm34 is a marker of progression and poor prognosis in human cancer.

Electronic supplementary material

The online version of this article (10.1186/s13048-019-0498-0) contains supplementary material, which is available to authorized users.

Leishmania donovani 90 kD Heat Shock Protein - Impact of Phosphosites on Parasite Fitness, Infectivity and Casein Kinase Affinity

Leishmania parasites are thought to control protein activity at the post-translational level, e.g. by protein phosphorylation. In the pathogenic amastigote, the mammalian stage of Leishmania parasites, heat shock proteins show increased phosphorylation, indicating a role in stage-specific signal transduction. Here we investigate the impact of phosphosites in the L. donovani heat shock protein 90. Using a chemical knock-down/genetic complementation approach, we mutated 11 confirmed or presumed phosphorylation sites and assessed the impact on overall fitness, morphology and in vitro infectivity. Most phosphosite mutations affected the growth and morphology of promastigotes in vitro, but with one exception, none of the phosphorylation site mutants had a selective impact on the in vitro infection of macrophages. Surprisingly, aspartate replacements mimicking the negative charge of phosphorylated serines or threonines had mostly negative impacts on viability and infectivity. HSP90 is a substrate for casein kinase 1.2-catalysed phosphorylation in vitro. While several putative phosphosite mutations abrogated casein kinase 1.2 activity on HSP90, only Ser289 could be identified as casein kinase target by mass spectrometry. In summary, our data show HSP90 as a downstream client of phosphorylation-mediated signalling in an organism that depends on post-transcriptional gene regulation.

β-TrCP upregulates HIF-1 in prostate cancer cells

The substantial availability of hypoxia-inducible factor 1 (HIF-1) for pathophysiological states, such as malignancies and ischemia, is primarily regulated post-translationally through the ubiquitin proteolytic system. The balance between degradation and stabilization of HIF-1α protein is determined by specific E3 ligases. In our search for new E3 ligases that might affect HIF-1α protein expression, we studied the effects of beta-transducin repeat-containing protein (β-TrCP) on the hypoxic pathway in cancer cells. β-TrCP is overexpressed in many tumors and regulates various cellular processes through mediating the degradation of important targets. Unexpectedly, we found that β-TrCP overexpression increases HIF-1α protein expression level as well as HIF-1 transcriptional activity by stabilizing HIF-1α protein and preventing its ubiquitination and proteasomal degradation in prostate cancer cells. By using a proteomic approach, we succeeded in demonstrating that β-TrCP interferes with the association between HIF-1α and HSP70/CHIP, a HIF-1α established E3 ligase complex. Whereas the E3 ligase activity of β-TrCP is well known, antagonizing another E3 ligase is a new mechanism of action of this important E3. We suggest that destroying or suppressing β-TrCP and thereby interrupting the HIF-1 pathway, could be valuable antitumor therapy.

Molecular cloning, characterization of Pomacea canaliculata HSP40 and its expression analysis under temperature change

Heat shock proteins (HSPs) play important roles in the adaption of Pomacea canaliculata to unsuitable environments. In the present study, a cDNA encoding HSP40 in P. canaliculata (PocaHSP40) was cloned and characterized. The PocaHSP40 cDNA was 1466 bp, containing an ORF of 954 bp encoding 317 amino acids. Bioinformatics analysis showed that PocaHSP40 belonged to type II HSP40s and had four predicted phosphorylation sites. Phylogenetic analysis proved the conservation of HSP40s in mollusks. PocaHSP40 was widely expressed in the gill, digestive gland, kidney, and foot muscle of P. canaliculata. Challenged by different temperatures, the expression of PocaHSP40 was up-regulated under low temperatures but not high temperatures, which was contrary to the expression change of PocaHSP70 under low and high temperatures. These results implied that P. canaliculata evolved different strategies for survival under low temperature and high temperature through the regulation of HSPs.

Utilization of HEPES for Enhancing Protein Transfection into Mammalian Cells

The delivery of active proteins into cells (protein transfection) for biological purposes offers considerable potential for clinical applications. Herein we demonstrate that, with a readily available, inexpensive organic agent, the 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) method can be used for simple and efficient protein transfection. By mixing proteins with a pure HEPES solution before they are applied to live cells, proteins with various molecular weights (including antibodies, recombinant proteins, and peptides) were successfully delivered into the cytoplasm of different cell types. The protein transfection efficiency of the HEPES method was not inferior to that of commercially available systems that are both more expensive and time consuming. Studies using endocytotic inhibitors and endosomal markers have revealed that cells internalize HEPES-protein mixtures through endocytosis. Results that HEPES-protein mixtures exhibited a low diffusion coefficient suggest that HEPES might neutralize the charges of proteins and, thus, facilitate their cellular internalization. Upon internalization, the cytosolic antibodies caused the degradation of targeted proteins in TRIM21-expressing cells. In summary, the HEPES method is efficient for protein transfection and has potential for myriad clinical applications.

Novel insights into molecular chaperone regulation of ribonucleotide reductase

The molecular chaperones Hsp70 and Hsp90 bind and fold a significant proportion of the proteome. They are responsible for the activity and stability of many disease-related proteins including those in cancer. Substantial effort has been devoted to developing a range of chaperone inhibitors for clinical use. Recent studies have identified the oncogenic ribonucleotide reductase (RNR) complex as an interactor of chaperones. While several generations of RNR inhibitor have been developed for use in cancer patients, many of these produce severe side effects such as nausea, vomiting and hair loss. Development of more potent, less patient-toxic anti-RNR strategies would be highly desirable. Inhibition of chaperones and associated co-chaperone molecules in both cancer and model organisms such as budding yeast result in the destabilization of RNR subunits and a corresponding sensitization to RNR inhibitors. Going forward, this may form part of a novel strategy to target cancer cells that are resistant to standard RNR inhibitors.

HSP70 Acetylation Prevents Combined mTORC1/2 Inhibitor and Curcumin Treatment-Induced Apoptosis

We previously reported that PP242 (dual inhibitor of mTORC1/2) plus curcumin induced apoptotic cell death through lysosomal membrane permeabilization (LMP)-mediated autophagy. However, the relationship between ER stress and apoptotic cell death by combined PP242 and curcumin treatment remains unknown. In the present study, we found that combined PP242 and curcumin treatment induced cytosolic Ca²⁺ release and ER stress. Interestingly, pretreatment with the chemical chaperones (TUDCA and 4-PBA) and knockdown of CHOP and ATF4 by siRNA did not abolish combined treatment-induced apoptosis in renal carcinoma cells. These results suggest that combined treatment with mTORC1/2 inhibitor and curcumin induces ER stress which is not essential for apoptotic cell death. Furthermore, overexpression of HSP70 significantly inhibited PP242 plus curcumin-induced LMP and apoptosis, but the protective effect was abolished by K77R mutation of acetylation site of HSP70. Taken together, our results reveal that regulation of HSP70 through K77 acetylation plays role in combined PP242 and curcumin treatment-induced apoptosis.

Highly polluted life history and acute heat stress, a hazardous mix for blue mussels

Intertidal sessile organisms constitute through their life history unintended stress recorders. This study focuses on the impact of pollution on Mytilus edulis ability to cope with an additional stress. For this purpose, two acclimation stages to different temperatures were conducted before an acute stress exposure in mussels collected from a heavily polluted site. Gill proteomes were analyzed by 2DE and regulated proteins identified. Massive mortality was observed for organisms acclimated to colder temperatures. Despite this major difference, both groups shared a common response with a strong representation of proteoforms corresponding to "folding, sorting and degradation" processes. Nevertheless, surviving mussels exhibit a marked increase in protein degradation consistent with the observed decrease of cell defense proteins. Mussels acclimated to warmer temperature response is essentially characterized by an improved heat shock response. These results show the differential ability of mussels to face both pollution and acute heat stress, particularly for low-acclimated organisms.

Genetic analysis of Hsp70 phosphorylation sites reveals a role in Candida albicans cell and colony morphogenesis

Heat shock proteins are best known for their role as chaperonins involved in general proteostasis, but they can also participate in specific cellular regulatory pathways, e.g. via their post-translational modification. Hsp70/Ssa1 is a central cytoplasmic chaperonin in eukaryotes, which also participates in cell cycle regulation via its phosphorylation at a specific residue. Here we analyze the role of Ssa1 phosphorylation in the morphogenesis of the fungus Candida albicans, a common human opportunistic pathogen. C. albicans can assume alternative yeast and hyphal (mold) morphologies, an ability that contributes to its virulence. We identified 11 phosphorylation sites on C. albicans Ssa1, of which 8 were only detected in the hyphal cells. Genetic analysis of these sites revealed allele-specific effects on growth or hyphae formation at 42 °C. Colony morphology, which is normally wrinkled or crenellated at 37 °C, reverted to smooth in several mutants, but this colony morphology phenotype was unrelated to cellular morphology. Two mutants exhibited a mild increase in sensitivity to the cell wall-active compounds caspofungin and calcofluor white. We suggest that this analysis could help direct screens for Ssa1-specific drugs to combat C. albicans virulence. The pleiotropic effects of many Ssa1 mutations are consistent with the large number of Ssa1 client proteins, whereas the lack of concordance between the phenotypes of the different alleles suggests that different sites on Ssa1 can affect interaction with specific classes of client proteins, and that modification of these sites can play cellular regulatory roles, consistent with the "chaperone code" hypothesis.

Intrinsic proteotoxic stress levels vary and act as a predictive marker for sensitivity of cancer cells to Hsp90 inhibition

Response of tumours to Hsp90 inhibitors is highly variable and their clinical effects are unpredictable, emphasising the need for a predictive marker. We postulated that sensitivity to Hsp90 inhibitors is connected to basal proteotoxic stress that makes cells dependent on Hsp90. Therefore, we assessed HSF1 as a general sensor of proteotoxic stress and correlated its activity with sensitivity to three separate small molecule Hsp90 inhibitors in seven breast cancer cell lines representing each of the different cancer subtypes. Flow cytometry was used to analyse the viability of breast cancer cell lines after Hsp90 inhibition. HSF1 activity was characterised by Ser326 phosphorylation and the transactivation capacity of HSF1 was determined by qPCR analysis of the ratios of HSF1-dependent (HOP, Hsp70) and HSF1-independent (CHIP) chaperones and cochaperone mRNAs. We show that the sensitivity of breast cancer cell lines to Hsp90 inhibition is highly variable. The basal levels of phosphorylated HSF1 also vary between cell lines and the magnitude of change in HSF1 phosphorylation after Hsp90 inhibition showed a negative correlation with sensitivity to Hsp90 inhibitors. Similarly, the basal transactivation capacity of HSF1, determined by the ratio of Hsp70 or HOP mRNA to CHIP mRNA level, is directly proportional to sensitivity to Hsp90 inhibitors. Increasing basal HSF1 activity by prior heat shock sensitised cells to Hsp90 inhibition. These results demonstrate that endogenous HSF1 activity varies between individual cancer cell lines and inversely reflects their sensitivity to Hsp90 inhibitors, suggesting that basal proteotoxic stress is an important and generalised predictor of response. Mechanistically, the data indicate that high endogenous proteotoxic stress levels sensitise to Hsp90 inhibition due to the inability to respond adequately to further proteotoxic stress. HSF1 activity therefore represents a potential biomarker for therapy with Hsp90 inhibitors, which may be useful for the rational design of future clinical studies.

Mitotic phosphorylation regulates Hsp72 spindle localization by uncoupling ATP binding from substrate release

Hsp72 is a member of the 70-kDa heat shock family of molecular chaperones (Hsp70s) that comprise a nucleotide-binding domain (NBD) and a substrate-binding domain (SBD) connected by a linker that couples the exchange of adenosine diphosphate (ADP) for adenosine triphosphate (ATP) with the release of the protein substrate. Mitotic phosphorylation of Hsp72 by the kinase NEK6 at Thr⁶⁶ located in the NBD promotes the localization of Hsp72 to the mitotic spindle and is required for efficient spindle assembly and chromosome congression and segregation. We determined the crystal structure of the Hsp72 NBD containing a genetically encoded phosphoserine at position 66. This revealed structural changes that stabilized interactions between subdomains within the NBD. ATP binding to the NBD of unmodified Hsp72 resulted in the release of substrate from the SBD, but phosphorylated Hsp72 retained substrate in the presence of ATP. Mutations that prevented phosphorylation-dependent subdomain interactions restored the connection between ATP binding and substrate release. Thus, phosphorylation of Thr⁶⁶ is a reversible mechanism that decouples the allosteric connection between nucleotide binding and substrate release, providing further insight into the regulation of the Hsp70 family. We propose that phosphorylation of Hsp72 on Thr⁶⁶ by NEK6 during mitosis promotes its localization to the spindle by stabilizing its interactions with components of the mitotic spindle.

Stress-induced phosphoprotein 1 acts as a scaffold protein for glycogen synthase kinase-3 beta-mediated phosphorylation of lysine-specific demethylase 1

Stress-induced phosphoprotein 1 (STIP1)-a co-chaperone of heat shock proteins-promotes cell proliferation and may act as an oncogenic factor. Similarly, glycogen synthase kinase-3 beta (GSK3β)-mediated phosphorylation of lysine-specific demethylase 1 (LSD1)-an epigenetic regulator-can contribute to the development of an aggressive cell phenotype. Owing to their ability to tether different molecules into functional complexes, scaffold proteins have a key role in the regulation of different signaling pathways in tumorigenesis. Here, we show that STIP1 acts as a scaffold promoting the interaction between LSD1 and GSK3β. Specifically, the TPR1 and TPR2B domains of STIP1 are capable of binding with the AOL domain of LSD1, whereas the TPR2A and TPR2B domains of STIP1 interact with the kinase domain of GSK3β. We also demonstrate that STIP1 is required for GSK3β-mediated LSD1 phosphorylation, which promoted LSD1 stability and enhanced cell proliferation. After transfection of cancer cells with double-mutant (S707A/S711A) LSD1, subcellular localization analysis revealed that LSD1 was translocated from the nucleus to the cytoplasm. In vitro experiments also showed that the LSD1 inhibitor SP2509 and the GSK3β inhibitor LY2090314 acted synergistically to induce cancer cell death. Finally, the immunohistochemical expression of STIP1 and LSD1 showed a positively correlation in human cancer specimens. In summary, our data provide mechanistic insights into the role of STIP1 in human tumorigenesis by showing that it serves as a scaffold for GSK3β-mediated LSD1 phosphorylation. The combination of LSD1 and GSK3β inhibitors may exert synergistic antitumor effects and deserves further scrutiny in preclinical studies.

Proteomic analysis of xylem vessel cell differentiation in VND7-inducible tobacco BY-2 cells by two-dimensional gel electrophoresis

The xylem vessel is an essential structure for water conduction in vascular plants. Xylem vessel cells deposit thick secondary cell walls and undergo programmed cell death, to function as water-conducting elements. Since the discovery of the plant-specific NAC domain-type VASCULAR-RELATED NAC-DOMAIN (VND) transcription factors, which function as master switches of xylem vessel cell differentiation in Arabidopsis, much has been learned about the transcriptional regulatory network of xylem vessel cell differentiation. However, little is known about proteome dynamics during xylem vessel cell differentiation. Here, we performed two-dimensional electrophoresis-based proteomic analysis of xylem vessel cell differentiation using a transgenic tobacco BY-2 cell line carrying the VND7-inducible system (BY-2/35S::VND7-VP16-GR), in which synchronous trans-differentiation into xylem vessel cells can be induced by the application of a glucocorticoid. Of the 47 spots revealed by gel electrophoresis, we successfully identified 40 proteins. Seventeen proteins, including several well-characterized proteins such as a cysteine protease and serine carboxypeptidase (involved in programmed cell death), were upregulated after 24 h of induction. However, previous transcriptomic analysis showed that only eight of these proteins are upregulated at the transcriptional level during xylem vessel cell differentiation in BY-2/35S::VND7-VP16-GR cells. These findings suggest that post-transcriptional regulation strongly affects proteomic dynamics during xylem vessel cell differentiation.

Regulation of the Hsp90 system

Hsp90 is a highly conserved and abundant chaperone. It participates in essential cellular activities by supporting the maturation process of its client proteins, many of which are protein kinases and steroid receptors. Client processing is achieved via extensive conformational changes within the dimeric chaperone. This requires an ATP hydrolysis activity that is controlled by auto-inhibitory mechanisms and several structurally diverse cofactors. Especially the client-specificity of Hsp90 depends on client-specific cofactors, which can adapt Hsp90's activities to the client requirements at different conditions and in different cell types. Additionally, post-translational modifications can influence almost every aspect of Hsp90's interactions and activities. In this review, we present these regulatory principles, discuss the factors that have an impact on Hsp90's function and elaborate the mechanisms that are responsible for regulating the Hsp90 machinery.

EGFR-TKI-induced HSP70 degradation and BER suppression facilitate the occurrence of the EGFR T790 M resistant mutation in lung cancer cells

Non-small cell lung cancer (NSCLC) patients harboring EGFR-activating mutations initially respond to EGFR tyrosine kinase inhibitors (EGFR-TKIs) and have shown favorable outcomes. However, acquired drug resistance to EGFR-TKIs develops in almost all patients mainly due to the EGFR T790 M mutation. Here, we show that treatment with low-dose EGFR-TKI results in the emergence of the EGFR T790 M mutation and in the reduction of HSP70 protein levels in HCC827 cells. Erlotinib treatment inhibits HSP70 phosphorylation at tyrosine 41 and increases HSP70 ubiquitination, resulting in HSP70 degradation. We show that EGFR-TKI treatment causes increased DNA damage and enhanced gene mutation rates, which are secondary to the EGFR-TKI-induced reduction of HSP70 protein. Importantly, HSP70 overexpression delays the occurrence of Erlotinib-induced EGFR T790 M mutation. We further demonstrate that HSP70 interacts with multiple enzymes in the base excision repair (BER) pathway and promotes not only the efficiency but also the fidelity of BER. Collectively, our findings show that EGFR-TKI treatment facilitates gene mutation and the emergence of EGFR T790 M secondary mutation by the attenuation of BER via induction of HSP70 protein degradation.

Detecting Posttranslational Modifications of Hsp90

The molecular chaperone Heat Shock Protein 90 (Hsp90) is essential in eukaryotes. Hsp90 chaperones proteins that are important determinants of multistep carcinogenesis. The chaperone function of Hsp90 is linked to its ability to bind and hydrolyze ATP. Co-chaperones as well as posttranslational modifications (phosphorylation, SUMOylation, and ubiquitination) are important for its stability and regulation of the ATPase activity. Both mammalian and yeast cells can be used to express and purify Hsp90 and also detect its posttranslational modifications by immunoblotting.

Constitutive redox and phosphoproteome changes in multiple herbicide resistant Avena fatua L. are similar to those of systemic acquired resistance and systemic acquired acclimation

Plants are routinely confronted with numerous biotic and abiotic stressors, and in response have evolved highly effective strategies of systemic acquired resistance (SAR) and systemic acquired acclimation (SAA), respectively. A much more evolutionarily recent abiotic stress is the application of herbicides to control weedy plants, and their intensive use has selected for resistant weed populations that cause substantial crop yield losses and increase production costs. Non-target site resistance (NTSR) to herbicides is rapidly increasing worldwide and is associated with alterations in generalized stress defense networks. This work investigated protein post-translational modifications associated with NTSR in multiple herbicide resistant (MHR) Avena fatua, and their commonalities with those of SAR and SAA. We used proteomic, biochemical, and immunological approaches to compare constitutive protein profiles in MHR and herbicide susceptible (HS) A. fatua populations. Phosphoproteome and redox proteome surveys showed that post-translational modifications of proteins with functions in core cellular processes were reduced in MHR plants, while those involved in xenobiotic and stress response, reactive oxygen species detoxification and redox maintenance, heat shock response, and intracellular signaling were elevated in MHR as compared to HS plants. More specifically, MHR plants contained constitutively elevated levels of three protein kinases including the lectin S-receptor-like serine/threonine-protein kinase LecRK2, a well-characterized component of SAR. Analyses of superoxide dismutase enzyme activity and protein levels did not reveal constitutive differences between MHR and HS plants. The overall results support the idea that herbicide stress is perceived similarly to other abiotic stresses, and that A. fatua NTSR shares analogous features with SAR and SAA. We speculate that MHR A. fatua's previous exposure to sublethal herbicide doses, as well as earlier evolution under a diversity of abiotic and biotic stressors, has led to a heightened state of stress preparedness that includes NTSR to a number of unrelated herbicides.

Icariin protects against ischemia‑reperfusion injury in H9C2 cells by upregulating heat shock protein 20

Icariin (ICA) has been implicated in certain biological and pathological processes, including myocardial ischemia/reperfusion (I/R) injury. The aim of the present study was to investigate the role of ICA in I/R‑induced cardiomyocyte injury and the potential underlying mechanism. Cell proliferation and apoptosis of H9C2 cells was determined by cell counting kit‑8 and flow cytometry assays. In addition, reactive oxygen species (ROS) production in H9C2 cells was measured by flow cytometry. Reverse transcription‑quantitative polymerase chain reaction and western blot assay were performed to examine the expression levels of proteins, including HSP20, B‑cell lymphoma 2 (Bcl‑2), cytochrome complex (Cyt‑c), apoptotic protease activating factor 1 (APAF1), caspase‑9 andcaspase‑3, and the phosphorylation of Akt (p‑Akt) in H9C2 cells. The present results demonstrated that, compared with the control group, the I/R group demonstrated significantly reduced levels of HSP20 expression and cell proliferation, and increased apoptosis and ROS production in H9C2 cells. In parallel, the expression levels of Cyt‑c, APAF1, caspase‑9 and caspase‑3 were significantly increased in the I/R group, although Bcl‑2 and p‑Akt/Akt expression levels were decreased. Furthermore, compared with the I/R group, ICA treatment and/or HSP20 overexpression significantly improved cardiac function, as evidenced by promoted cell proliferation and inhibited apoptosis of H9C2 cells. The current study indicates that ICA exerts a cardioprotective effect against I/R injury, which is associated with the upregulation of HSP20.

Cdc7-Dbf4-mediated phosphorylation of HSP90-S164 stabilizes HSP90-HCLK2-MRN complex to enhance ATR/ATM signaling that overcomes replication stress in cancer

Cdc7-Dbf4 kinase plays a key role in the initiation of DNA replication and contributes to the replication stress in cancer. The activity of human Cdc7-Dbf4 kinase remains active and acts as an effector of checkpoint under replication stress. However, the downstream targets of Cdc7-Dbf4 contributed to checkpoint regulation and replication stress-support function in cancer are not fully identified. In this work, we showed that aberrant Cdc7-Dbf4 induces DNA lesions that activate ATM/ATR-mediated checkpoint and homologous recombination (HR) DNA repair. Using a phosphoproteome approach, we identified HSP90-S164 as a target of Cdc7-Dbf4 in vitro and in vivo. The phosphorylation of HSP90-S164 by Cdc7-Dbf4 is required for the stability of HSP90-HCLK2-MRN complex and the function of ATM/ATR signaling cascade and HR DNA repair. In clinically, the phosphorylation of HSP90-S164 indeed is increased in oral cancer patients. Our results indicate that aberrant Cdc7-Dbf4 enhances replication stress tolerance by rewiring ATR/ATM mediated HR repair through HSP90-S164 phosphorylation and by promoting recovery from replication stress. We provide a new solution to a subtyping of cancer patients with dominant ATR/HSP90 expression by combining inhibitors of ATR-Chk1, HSP90, or Cdc7 in cancer combination therapy.

Targeting STUB1-tissue factor axis normalizes hyperthrombotic uremic phenotype without increasing bleeding risk

Chronic kidney disease (CKD/uremia) remains vexing because it increases the risk of atherothrombosis and is also associated with bleeding complications on standard antithrombotic/antiplatelet therapies. Although the associations of indolic uremic solutes and vascular wall proteins [such as tissue factor (TF) and aryl hydrocarbon receptor (AHR)] are being defined, the specific mechanisms that drive the thrombotic and bleeding risks are not fully understood. We now present an indolic solute-specific animal model, which focuses on solute-protein interactions and shows that indolic solutes mediate the hyperthrombotic phenotype across all CKD stages in an AHR- and TF-dependent manner. We further demonstrate that AHR regulates TF through STIP1 homology and U-box-containing protein 1 (STUB1). As a ubiquitin ligase, STUB1 dynamically interacts with and degrades TF through ubiquitination in the uremic milieu. TF regulation by STUB1 is supported in humans by an inverse relationship of STUB1 and TF expression and reduced STUB1-TF interaction in uremic vessels. Genetic or pharmacological manipulation of STUB1 in vascular smooth muscle cells inhibited thrombosis in flow loops. STUB1 perturbations reverted the uremic hyperthrombotic phenotype without prolonging the bleeding time, in contrast to heparin, the standard-of-care antithrombotic in CKD patients. Our work refines the thrombosis axis (STUB1 is a mediator of indolic solute-AHR-TF axis) and expands the understanding of the interconnected relationships driving the fragile thrombotic state in CKD. It also establishes a means of minimizing the uremic hyperthrombotic phenotype without altering the hemostatic balance, a long-sought-after combination in CKD patients.

Cracking the Chaperone Code: Cellular Roles for Hsp70 Phosphorylation

Heat shock protein 70 (Hsp70) is a molecular chaperone required for protein folding, cell viability, and cancer cell proliferation. Recent studies suggest that Hsp70 phosphorylation regulates important cellular processes, such as cell cycle progression, apoptosis, protein degradation, and resistance to anticancer therapeutics.

CHIP as a membrane-shuttling proteostasis sensor

Cells respond to protein misfolding and aggregation in the cytosol by adjusting gene transcription and a number of post-transcriptional processes. In parallel to functional reactions, cellular structure changes as well; however, the mechanisms underlying the early adaptation of cellular compartments to cytosolic protein misfolding are less clear. Here we show that the mammalian ubiquitin ligase C-terminal Hsp70-interacting protein (CHIP), if freed from chaperones during acute stress, can dock on cellular membranes thus performing a proteostasis sensor function. We reconstituted this process in vitro and found that mainly phosphatidic acid and phosphatidylinositol-4-phosphate enhance association of chaperone-free CHIP with liposomes. HSP70 and membranes compete for mutually exclusive binding to the tetratricopeptide repeat domain of CHIP. At new cellular locations, access to compartment-specific substrates would enable CHIP to participate in the reorganization of the respective organelles, as exemplified by the fragmentation of the Golgi apparatus (effector function).

Role of protein kinases CK1α and CK2 in multiple myeloma: regulation of pivotal survival and stress-managing pathways

Multiple myeloma (MM) is a malignant tumor of transformed plasma cells. MM pathogenesis is a multistep process. This cancer can occur de novo (rarely) or it can develop from monoclonal gammopathy of undetermined significance (most of the cases). MM can be asymptomatic (smoldering myeloma) or clinically active. Malignant plasma cells exploit intrinsic and extrinsic bone marrow microenvironment-derived growth signals. Upregulation of stress-coping pathways is also instrumental to maintain MM cell growth. The phylogenetically related Ser/Thr kinases CSNK1A1 (CK1α) and CSNK2 (CK2) have recently gained a growing importance in hematologic malignancies arising both from precursors and from mature blood cells. In multiple myeloma, CK1α or CK2 sustain oncogenic cascades, such as the PI3K/AKT, JAK/STAT, and NF-κB, as well as propel stress-related signaling that help in coping with different noxae. Data also suggest that these kinases modulate the delivery of growth factors and cytokines from the bone marrow stroma. The “non-oncogene addiction” phenotype generated by the increased activity of CK1α and CK2 in multiple myeloma contributes to malignant plasma cell proliferation and survival and represents an Achilles’ heel for the activity of small ATP competitive CK1α or CK2 inhibitors.

Hsp70's RNA-binding and mRNA-stabilizing activities are independent of its protein chaperone functions

Hsp70 is a protein chaperone that prevents protein aggregation and aids protein folding by binding to hydrophobic peptide domains through a reversible mechanism directed by an ATPase cycle. However, Hsp70 also binds U-rich RNA including some AU-rich elements (AREs) that regulate the decay kinetics of select mRNAs and has recently been shown to bind and stabilize some ARE-containing transcripts in cells. Previous studies indicated that both the ATP- and peptide-binding domains of Hsp70 contributed to the stability of Hsp70-RNA complexes and that ATP might inhibit RNA recruitment. This suggested the possibility that RNA binding by Hsp70 might mimic features of its peptide-directed chaperone activities. Here, using purified, cofactor-free preparations of recombinant human Hsp70 and quantitative biochemical approaches, we found that high-affinity RNA binding requires at least 30 nucleotides of RNA sequence but is independent of Hsp70's nucleotide-bound status, ATPase activity, or peptide-binding roles. Furthermore, although both the ATP- and peptide-binding domains of Hsp70 could form complexes with an ARE sequence from VEGFA mRNA in vitro, only the peptide-binding domain could recover cellular VEGFA mRNA in ribonucleoprotein immunoprecipitations. Finally, Hsp70-directed stabilization of VEGFA mRNA in cells was mediated exclusively by the protein's peptide-binding domain. Together, these findings indicate that the RNA-binding and mRNA-stabilizing functions of Hsp70 are independent of its protein chaperone cycle but also provide potential mechanical explanations for several well-established and recently discovered cytoprotective and RNA-based Hsp70 functions.

Targeting Hsp27/eIF4E interaction with phenazine compound: a promising alternative for castration-resistant prostate cancer treatment

The actual strategy to improve current therapies in advanced prostate cancer involves targeting genes activated by androgen withdrawal, either to delay or prevent the emergence of the castration-refractory phenotype. However, these genes are often implicated in several physiological processes, and long-term inhibition of survival proteins might be accompanied with cytotoxic effects. To avoid this problem, an alternative therapeutic strategy relies on the identification and use of compounds that disrupt specific protein-protein interactions involved in androgen withdrawal. Specifically, the interaction of the chaperone protein Hsp27 with the initiation factor eIF4E leads to the protection of protein synthesis initiation process and enhances cell survival during cell stress induced by castration or chemotherapy. Thus, in this work we aimed at i) identifying the interaction site of the Hsp27/eIF4E complex and ii) interfere with the relevant protein/protein association mechanism involved in castration-resistant progression of prostate cancer. By a combination of experimental and modeling techniques, we proved that eIF4E interacts with the C-terminal part of Hsp27, preferentially when Hsp27 is phosphorylated. We also observed that the loss of this interaction increased cell chemo-and hormone-sensitivity. In order to find a potential inhibitor of Hsp27/eIF4E interaction, BRET assays in combination with molecular simulations identified the phenazine derivative 14 as the compound able to efficiently interfere with this protein/protein interaction, thereby inhibiting cell viability and increasing cell death in chemo- and castration-resistant prostate cancer models in vitro and in vivo.

Carboxy-terminus Hsc70 interacting protein exerts a tumor inhibition function in head and neck cancer

Several independent studies have reported the roles of the E3 ubiquitin ligase, carboxy-terminus Hsc70 interacting protein (CHIP) in various types of cancers. However, the biological effects of CHIP vary in regards to different cancers, and the role of CHIP in head and neck cancers (HNCs) remains unknown. In the present study, CHIP overexpression plasmids and CHIP knockdown lentivirus were constructed to affect the expression levels of CHIP protein and biological behaviors in HNC cell lines bilaterally. The biological behaviors regulated by CHIP in HNCs were investigated both in vivo and in vitro with a series of assays and analyses. A tissue microarray was stained and analyzed for the clinical significance of CHIP expression in HNCs. We identified that CHIP suppressed the malignant behaviors of HNCs in a series of in vitro and in vivo experiments, but not its two loss-of-function mutants. However, we observed an altered expression pattern of CHIP from a well, moderate, to poor differentiation pathological status in HNC specimens. In a retrospective cohort of HNCs, lower expression of CHIP indicated a poor differentiation status in tumors and a lower overall survival rate. The present study demonstrated that CHIP functions as a tumor suppressor in HNCs. In conclusion, we demonstrated that suppressed expression of CHIP may result in the progression of HNCs.

Significant and unique changes in phosphorylation levels of four phosphoproteins in two apple rootstock genotypes under drought stress

Drought stress is a major problem around the world and there is still little molecular mechanism about how fruit crops deal with moderate drought stress. Here, the physiological and phosphoproteomic responses of drought-sensitive genotype (M26) and drought-tolerant genotype (MBB) under moderate drought stress were investigated. Our results of the physiology analysis indicated that the MBB genotype could produce more osmosis-regulating substances. Furthermore, phosphoproteins from leaves of both genotypes under moderate drought stress were analyzed using the isobaric tags for relative and absolute quantification technology. A total of 595 unique phosphopeptides, 682 phosphorylated sites, and 446 phosphoproteins were quantitatively analyzed in the two genotypes. Five and thirty-five phosphoproteins with the phosphorylation levels significantly changed (PLSC) were identified in M26 and MBB, respectively. Among these, four PLSC phosphoproteins were common to both genotypes, perhaps indicating a partial overlap of the mechanisms to moderate drought stress. Gene ontology analyses revealed that the PLSC phosphoproteins represent a unique combination of metabolism, transcription, translation, and protein processing, suggesting that the response in apple to moderate drought stress encompasses a new and unique homeostasis of major cellular processes. The basic trend was an increase in protein and organic molecules abundance related to drought. These increases were higher in MBB than in M26. Our study is the first to address the phosphoproteome of apple rootstocks in response to moderate drought stress, and provide insights into the molecular regulation mechanisms of apple rootstock under moderate drought stress.

Lys48 ubiquitination during the intraerythrocytic cycle of the rodent malaria parasite, Plasmodium chabaudi

Ubiquitination tags proteins for different functions within the cell. One of the most abundant and studied ubiquitin modification is the Lys48 polyubiquitin chain that modifies proteins for their destruction by proteasome. In Plasmodium is proposed that post-translational regulation is fundamental for parasite development during its complex life-cycle; thus, the objective of this work was to analyze the ubiquitination during Plasmodium chabaudi intraerythrocytic stages. Ubiquitinated proteins were detected during intraerythrocytic stages of Plasmodium chabaudi by immunofluorescent microscopy, bidimensional electrophoresis (2-DE) combined with immunoblotting and mass spectrometry. All the studied stages presented protein ubiquitination and Lys48 polyubiquitination with more abundance during the schizont stage. Three ubiquitinated proteins were identified for rings, five for trophozoites and twenty for schizonts. Only proteins detected with a specific anti- Lys48 polyubiquitin antibody were selected for Mass Spectrometry analysis and two of these identified proteins were selected in order to detect the specific amino acid residues where ubiquitin is placed. Ubiquitinated proteins during the ring and trophozoite stages were related with the invasion process and in schizont proteins were related with nucleic acid metabolism, glycolysis and protein biosynthesis. Most of the ubiquitin detection was during the schizont stage and the Lys48 polyubiquitination during this stage was related to proteins that are expected to be abundant during the trophozoite stage. The evidence that these Lys48 polyubiquitinated proteins are tagged for destruction by the proteasome complex suggests that this type of post-translational modification is important in the regulation of protein abundance during the life-cycle and may also contribute to the parasite cell-cycle progression.

Mechanisms of Hsp90 regulation

Heat shock protein 90 (Hsp90) is a molecular chaperone that is involved in the activation of disparate client proteins. This implicates Hsp90 in diverse biological processes that require a variety of co-ordinated regulatory mechanisms to control its activity. Perhaps the most important regulator is heat shock factor 1 (HSF1), which is primarily responsible for upregulating Hsp90 by binding heat shock elements (HSEs) within Hsp90 promoters. HSF1 is itself subject to a variety of regulatory processes and can directly respond to stress. HSF1 also interacts with a variety of transcriptional factors that help integrate biological signals, which in turn regulate Hsp90 appropriately. Because of the diverse clientele of Hsp90 a whole variety of co-chaperones also regulate its activity and some are directly responsible for delivery of client protein. Consequently, co-chaperones themselves, like Hsp90, are also subject to regulatory mechanisms such as post translational modification. This review, looks at the many different levels by which Hsp90 activity is ultimately regulated.

Heat Shock Protein (HSP) Drug Discovery and Development: Targeting Heat Shock Proteins in Disease

Heat shock proteins (HSPs) present as a double edged sword. While they play an important role in maintaining protein homeostasis in a normal cell, cancer cells have evolved to co-opt HSP function to promote their own survival. As a result, HSPs such as HSP90 have attracted a great deal of interest as a potential anticancer target. These efforts have resulted in over 20 distinct compounds entering clinical evaluation for the treatment of cancer. However, despite the potent anticancer activity demonstrated in preclinical models, to date no HSP90 inhibitor has obtained regulatory approval. In this review we discuss the unique challenges faced in targeting HSPs that have likely contributed to their lack of progress in the clinic and suggest ways to overcome these so that the enormous potential of these compounds to benefit patients can finally be realized. We also provide a guideline for the future development of HSP-targeted agents based on the many lessons learned during the last two decades in developing HSP90 inhibitors.

Regulatory Mechanisms of Hsp90

The ability of Hsp90 to activate a disparate clientele implicates this chaperone in diverse biological processes. To accommodate such varied roles, Hsp90 requires a variety of regulatory mechanisms that are coordinated in order to modulate its activity appropriately. Amongst these, the master-regulator heat shock factor 1 (HSF1) is critically important in upregulating Hsp90 during stress, but is also responsible, through interaction with specific transcription factors (such as STAT1 and Strap/p300) for the integration of a variety of biological signals that ultimately modulate Hsp90 expression. Additionally, transcription factors, such as STAT1, STAT3 (including STAT1-STAT3 oligomers), NF-IL6, and NF-kB, are known to influence Hsp90 expression directly. Co-chaperones offer another mechanism for Hsp90 regulation, and these can modulate the chaperone cycle appropriately for specific clientele. Co-chaperones include those that deliver specific clients to Hsp90, and others that regulate the chaperone cycle for specific Hsp90-client complexes by modulating Hsp90s ATPase activity. Finally, post-translational modification (PTM) of Hsp90 and its co-chaperones helps too further regulate the variety of different Hsp90 complexes found in cells.

How Studies of the Serotonin System in Macaque Models of Menopause Relate to Alzheimer's Disease1

Serotonin plays a key role in mood or affect, and dysfunction of the serotonin system has been linked to depression in humans and animal models. Depression appears prior to or coincident with overt symptoms of Alzheimer's disease (AD) in about 50% of patients, and some experts consider it a risk factor for the development of AD. In addition, AD is more prevalent in women, who also show increased incidence of depression. Indeed, it has been proposed that mechanisms underlying depression overlap the mechanisms thought to hasten AD. Women undergo ovarian failure and cessation of ovarian steroid production in middle age and the postmenopausal period correlates with an increase in the onset of depression and AD. This laboratory has examined the many actions of ovarian steroids in the serotonin system of non-human primates using a rhesus macaque model of surgical menopause with short or long-term estradiol (E) or estradiol plus progesterone (E+P) replacement therapy. In this mini-review, we present a brief synopsis of the relevant literature concerning AD, depression, and serotonin. We also present some of our data on serotonin neuron viability, the involvement of the caspase-independent pathway, and apoptosis-inducing factor in serotonin-neuron viability, as well as gene expression related to neurodegeneration and neuron viability in serotonin neurons from adult and aged surgical menopausal macaques. We show that ovarian steroids, particularly E, are crucial for serotonin neuron function and health. In the absence of E, serotonin neurons are endangered and deteriorating toward apoptosis. The possibility that this scenario may proceed or accompany AD in postmenopausal women seems likely.

Unraveling the CHIP:Hsp70 complex as an information processor for protein quality control

The CHIP:Hsp70 complex stands at the crossroads of the cellular protein quality control system. Hsp70 facilitates active refolding of misfolded client proteins, while CHIP directs ubiquitination of misfolded client proteins bound to Hsp70. The direct competition between CHIP and Hsp70 for the fate of misfolded proteins leads to the question: how does the CHIP:Hsp70 complex execute triage decisions that direct misfolded proteins for either refolding or degradation? The current body of literature points toward action of the CHIP:Hsp70 complex as an information processor that takes inputs in the form of client folding state, dynamics, and posttranslational modifications, then outputs either refolded or ubiquitinated client proteins. Herein we examine the CHIP:Hsp70 complex beginning with the structure and function of CHIP and Hsp70, followed by an examination of recent studies of the interactions and dynamics of the CHIP:Hsp70 complex.

Chemical Tools to Investigate Mechanisms Associated with HSP90 and HSP70 in Disease

The chaperome is a large and diverse protein machinery composed of chaperone proteins and a variety of helpers, such as the co-chaperones, folding enzymes, and scaffolding and adapter proteins. Heat shock protein 90s and 70s (HSP90s and HSP70s), the most abundant chaperome members in human cells, are also the most complex. As we have learned to appreciate, their functions are context dependent and manifested through a variety of conformations that each recruit a subset of co-chaperone, scaffolding, and folding proteins and which are further diversified by the posttranslational modifications each carry, making their study through classic genetic and biochemical techniques quite a challenge. Chemical biology tools and techniques have been developed over the years to help decipher the complexities of the HSPs and this review provides an overview of such efforts with focus on HSP90 and HSP70.

Leukocyte immunoglobulin-like receptor B4 regulates key signalling molecules involved in FcγRI-mediated clathrin-dependent endocytosis and phagocytosis

FcγRI cross-linking on monocytes may trigger clathrin-mediated endocytosis, likely through interaction of multiple intracellular molecules that are controlled by phosphorylation and dephosphorylation events. However, the identity of phospho-proteins and their regulation are unknown. We proposed the leukocyte immunoglobulin-like receptor B4 (LILRB4) that inhibits FcγRI-mediated cytokine production via Tyr dephosphorylation of multiple kinases, may also regulate endocytosis/phagocytosis through similar mechanisms. FcγRI and/or LILRB4 were antibody-ligated on THP-1 cells, lysates immunoprecipitated using anti-pTyr antibody and peptides sequenced by mass spectrometry. Mascot Search identified 25 Tyr phosphorylated peptides with high confidence. Ingenuity Pathway Analysis revealed that the most significantly affected pathways were clathrin-mediated endocytosis and Fc-receptor dependent phagocytosis. Tyr phosphorylation of key candidate proteins in these pathways included common γ-chain of the Fc receptors, Syk, clathrin, E3 ubiquitin protein ligase Cbl, hepatocyte growth factor-regulated tyrosine kinase substrate, tripartite motif-containing 21 and heat shock protein 70. Importantly, co-ligation of LILRB4 with FcγRI caused significant dephosphorylation of these proteins and was associated with suppression of Fc receptor-dependent uptake of antibody-opsonised bacterial particles, indicating that LILRB4. These results suggest that Tyr phosphorylation may be critical in FcγRI-dependent endocytosis/phagocytosis that may be regulated by LILRB4 by triggering dephosphorylation of key signalling proteins.

ARD1-mediated Hsp70 acetylation balances stress-induced protein refolding and degradation

Heat shock protein (Hsp)70 is a molecular chaperone that maintains protein homoeostasis during cellular stress through two opposing mechanisms: protein refolding and degradation. However, the mechanisms by which Hsp70 balances these opposing functions under stress conditions remain unknown. Here, we demonstrate that Hsp70 preferentially facilitates protein refolding after stress, gradually switching to protein degradation via a mechanism dependent on ARD1-mediated Hsp70 acetylation. During the early stress response, Hsp70 is immediately acetylated by ARD1 at K77, and the acetylated Hsp70 binds to the co-chaperone Hop to allow protein refolding. Thereafter, Hsp70 is deacetylated and binds to the ubiquitin ligase protein CHIP to complete protein degradation during later stages. This switch is required for the maintenance of protein homoeostasis and ultimately rescues cells from stress-induced cell death in vitro and in vivo. Therefore, ARD1-mediated Hsp70 acetylation is a regulatory mechanism that temporally balances protein refolding/degradation in response to stress.

The chaperone Hsp70 has a dual role, promoting both protein refolding and protein degradation. Seo and Park et al. show that Hsp70 acetylation enhances protein refolding after stress, and that subsequent deacetylation progressively promotes ubiquitin ligase binding and protein degradation.

HSP70 regulates the function of mitotic centrosomes

To establish a functional bipolar mitotic spindle, the centrosome expands and matures, acquiring enhanced activities for microtubule (MT) nucleation and assembly at the onset of mitosis. However, the regulatory mechanisms of centrosome maturation and MT assembly from the matured centrosome are largely unknown. In this study, we showed that heat shock protein (HSP) 70 considerably accumulates at the mitotic centrosome during prometaphase to metaphase and is required for bipolar spindle assembly. Inhibition or depletion of HSP70 impaired the function of mitotic centrosome and disrupted MT nucleation and polymerization from the spindle pole, and may thus result in formation of abnormal mitotic spindles. In addition, HSP70 may associate with NEDD1 and γ-tubulin, two pericentriolar material (PCM) components essential for centrosome maturation and MT nucleation. Loss of HSP70 function disrupted the interaction between NEDD1 and γ-tubulin, and reduced their accumulation at the mitotic centrosome. Our results thus demonstrate a role for HSP70 in regulating centrosome integrity during mitosis, and indicate that HSP70 is required for the maintenance of a functional mitotic centrosome that supports the assembly of a bipolar mitotic spindle.

The molecular chaperone Hsp70 promotes the proteolytic removal of oxidatively damaged proteins by the proteasome

One hallmark of aging is the accumulation of protein aggregates, promoted by the unfolding of oxidized proteins. Unraveling the mechanism by which oxidized proteins are degraded may provide a basis to delay the early onset of features, such as protein aggregate formation, that contribute to the aging phenotype. In order to prevent aggregation of oxidized proteins, cells recur to the 20S proteasome, an efficient turnover proteolysis complex. It has previously been shown that upon oxidative stress the 26S proteasome, another form, dissociates into the 20S form. A critical player implicated in its dissociation is the Heat Shock Protein 70 (Hsp70), which promotes an increase in free 20S proteasome and, therefore, an increased capability to degrade oxidized proteins. The aim of this study was to test whether or not Hsp70 is involved in cooperating with the 20S proteasome for a selective degradation of oxidatively damaged proteins. Our results demonstrate that Hsp70 expression is induced in HT22 cells as a result of mild oxidative stress conditions. Furthermore, Hsp70 prevents the accumulation of oxidized proteins and directly promotes their degradation by the 20S proteasome. In contrast the expression of the Heat shock cognate protein 70 (Hsc70) was not changed in recovery after oxidative stress and Hsc70 has no influence on the removal of oxidatively damaged proteins. We were able to demonstrate in HT22 cells, in brain homogenates from 129/SV mice and in vitro, that there is an increased interaction of Hsp70 with oxidized proteins, but also with the 20S proteasome, indicating a role of Hsp70 in mediating the interaction of oxidized proteins with the 20S proteasome. Thus, our data clearly implicate an involvement of Hsp70 oxidatively damaged protein degradation by the 20S proteasome.

Determining protein biomarkers for DLBCL using FFPE tissues from HIV negative and HIV positive patients

DLBCL is the most common lymphoma subtype occurring in older populations as well as in younger HIV infected patients. The current treatment options for DLBCL are effective for most patients yet the relapse rate is high. While many biomarkers for DLBCL exist, they are not in clinical use due to low sensitivity and specificity. In addition, these biomarkers have not been studied in the HIV context. Therefore, the identification of new biomarkers for HIV negative and HIV positive DLBCL, may lead to a better understanding of the disease pathology and better therapeutic design. Protein biomarkers for DLBCL were determined using MALDI imaging mass spectrometry (IMS) and characterised using LC-MS. The expression of one of the biomarkers, heat shock protein (Hsp) 70, was confirmed on a separate cohort of samples using immunohistochemistry. The biomarkers identified in the study consisted of four protein clusters including glycolytic enzymes, ribosomal proteins, histones and collagen. These proteins could differentiate between control and tumour tissue, and the DLBCL immunohistochemical subtypes in both cohorts. The majority (41/52) of samples in the confirmation cohort were negative for Hsp70 expression. The HIV positive DLBCL cases had a higher percentage of cases expressing Hsp70 than their HIV negative counterparts. The non-GC subtype also frequently overexpressed Hsp70, confirming MALDI IMS data. The expression of Hsp70 did not correlate with survival in both the HIV negative and HIV positive cohort. This study identified potential biomarkers for HIV negative and HIV positive DLBCL from FFPE tissue sections. These may be used as diagnostic and prognostic markers complementary to current clinical management programmes for DLBCL.